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What is clean steel?
Clan steel refers to steel which is free from inclusions. Inclusions are non metallic particles embedded in the steel matrix. Practically it is not possible to produce steel without any inclusion. Therefore we can talk about cleaner steel. Which steel is clean would depend on the applications. In this connection it is important to know that there is a limiting size below which inclusion does not affect mechanical property. Table lists some applications which can tolerate some minimum inclusions size:
Steel product |
Allowed impurity in ppm |
Allowed size |
Automotive and deep drawing sheet |
C<30, N<30 |
100 |
Line pipes |
S<30, N<50, TO<30 |
100 |
Bearings |
TO<10 |
15 |
Tire cord |
H<2N<40, TO<15 |
10 |
Heavy plate steels |
H<2 N+30 to 40, TO<20 |
13 |
Wires |
N<40, TO<15 |
20 |
Drawn and ironed cans |
C<30, N<40, TO<20 |
20 |
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Types of inclusions:
Inclusions are chemical compounds of metals like (Fe, Mn, Al, Si, Ca etc) with non metals (O, S, N, C, H). Different types are:
- Oxides:
- Sulphides:
 ,Nitirides:  etc.
- Oxysulphides:
 etc.
- Carbonitrides: Titanium/ vanadium/Niobium carbonitirides, etc.
- Phosphides:
By mineralogical content, oxygen inclusions are classified:
- Free oxides -
 (corundum) and other;
- Spinels – Ferrites, chromites and aluminates.
- Silicates-
 with a mixture of iron, manganese, chromium, aluminum and tungsten oxides and also crystalline silicates.
By stability, non –metallic inclusions are rather stable or unstable. Unstable inclusions are iron and manganese sulfides and also some free oxides.
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